Trypanosoma cruzi

Question 1

How is T. cruzi classified?

Answer 1

Protozoa: Flagellates

Question 2

How is T. cruzi transmitted?

Answer 2

Contact of the bitten area with the feces or urine of the Triatomine bug (the kissing bug)

Other ways (rare): blood transfusion, organ transplantation, transplacentally, laboratory accidents, contaminated food and water

Question 3

What is the life cycle of T. cruzi?

Answer 3

1. Triatomine bug takes a blood meal in vertebrae’s (humans) and passes metacyclic trypomastigotes in feces, trypomastigotes enter bite wound or mucosal membrane such as the conjunctiva (eye)
2. Metacyclic trypomastigotes penetrate various cells at bite wound site (e.g. fibroblast, muscle cells, and macrophages). Inside cells they transform into intracellular amastigotes
3. Amastigotes multiply by binary fission (asexual) of infected tissues - then differentiate into trypomastigotes and released into the circulation as bloodstream trypomastigotes. Here it can infect other cells and transform into intracellular amastigotes in new infection sides or
4. The triatomine bug takes blood meal and trypomastigotes are ingested by the triatomine bug
5. Trypomastigotes are broken down in the stomach of the bug. Th surviving trypomastigotes transform into epimastigotes and arrive to the midgut
6. In the midgut of the bug they multiply
7. In the midgut the transformation from non-infactive epimastigotes to infective metacyclic trypomastigotes takes place. After this process they can bite new hosts and infect them again

Question 4

What type of life cycle does T. cruzi have? And type of hosts?

Answer 4

Indirect life cycle

human intermediate host

Question 5

What are other reservoirs of T. cruzi?

Answer 5

armadillos possums racoons woodrats other rodents and domestic dogs

Question 6

What are symptoms of T. cruzi?

Answer 6

2 phases of Chagas
Acute phase (1-2 weeks)
- often asymptomatic
- some symptoms: fatigue, body 
  ache, diarrhoea, vomiting and 
  Romana's sign (swelling of the eye 
  lid at the side of the bite). 
- high number of parasites in the 
  blood

It is not self limiting - untreated will progress to the chronic stage

Chronic phase ( appr. after 8 weeks)
- often asymptomatic
- symptoms: gastrointestinal 
  complication, cardiac implications
- can be fetal
- low parasitemia - not found circulating in blood

Question 7

Where is T. cruzi endemic?

Answer 7

Middle and South America

Question 8

How is T. cruzi diagnosed?

Answer 8

Acute phase
- microscopy: detects parasites in 
  bloodstream
- Molecular diagnosis
- PCR

Chronic phase
- serological test (enzyme immunoassay, immunoblot and IFA): detects antibodies of the parasite

The standard approach is to use 2 or more different test that looks at multiple antibodies or antigens - you can look for trypomastigotes in the bloodstream or intracellular amastigotes

Question 9

So which form of T. cruzi is inside the cell and outside the cell

Answer 9

Outside - Trypomastigote form

Inside - Amastigote form

Question 10

What is the infective stage of T. cruzi?

Answer 10

trypomastigote form

Question 11

What is the diagnostic form of T. cruzi?

Answer 11

Intracellular amastigotes and trypomastigotes